Hi Michael,
I believe your post condition should read {:post [(number? %)]}.
Thanks,
Ambrose
On Fri, Jul 25, 2014 at 6:56 AM, Michael O'Keefe <[email protected]
> wrote:
> Hello All,
>
> I encountered the following behavior in Clojure 1.6 and wanted to check if
> it should be considered a bug or not. I would say yes but wanted to double
> check on the list first.
>
> Here's a minimal test case that elicited the error:
>
> (defn f
>
> [xs acc]
> (if (nil? xs)
> acc
> (recur (next xs) (+ (first xs) acc))))
>
> (f [1 2 3 4] 0) => 10
>
>
> Now, if I want to add pre/post conditions, the following happens:
>
> (defn g
>
> [xs acc]
> {:pre [(or (nil? xs) (sequential? xs)) (number? acc)]
> :post [number?]}
> (if (nil? xs)
> acc
> (recur (next xs) (+ (first xs) acc))))
>
>
> => this fails to compile with "CompilerException
> java.lang.UnsupportedOperationException: Can only recur from tail position"
>
>
> In fact, it is only the post-condition that triggers the issue.
>
> My guess would be that the recur statement is being knocked out of tail
> position by the mechanism for handling the post-condition assertion. It can
> be fixed in the code by adding an explicit loop:
>
> (defn g2 [xs acc]
> {:pre [(or (nil? xs) (sequential? xs)) (number? acc)]
> :post [number?]}
> (loop [xs xs
> acc acc]
> (if (nil? xs)
> acc
> (recur (next xs) (+ (first xs) acc)))))
>
>
> Thanks,
>
> Michael O'Keefe
>
> --
> You received this message because you are subscribed to the Google
> Groups "Clojure" group.
> To post to this group, send email to [email protected]
> Note that posts from new members are moderated - please be patient with
> your first post.
> To unsubscribe from this group, send email to
> [email protected]
> For more options, visit this group at
> http://groups.google.com/group/clojure?hl=en
> ---
> You received this message because you are subscribed to the Google Groups
> "Clojure" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to [email protected].
> For more options, visit https://groups.google.com/d/optout.
>
--
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to [email protected]
Note that posts from new members are moderated - please be patient with your
first post.
To unsubscribe from this group, send email to
[email protected]
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en
---
You received this message because you are subscribed to the Google Groups
"Clojure" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
For more options, visit https://groups.google.com/d/optout.
